Pitts is an all-catch, no-block TE. We already have one of those in Gesecki (who we're going to have to pay next offseason) and you can't play two. If you decide Pitts is a WR, he duplicates the traits we already have on the outside -- big, good leapers, no lateral separation. He doesn't fit with the roster to which we have already committed, which diminishes the chances he'll be the top-15 starter as a rookie that you need him to be.
And back to the money. The NFL has a hard salary cap. When you spend more at a no -premium position, you have to dig through the bargain bin at the premium positions. Teams that are successful get surplus value from players on their rookie contracts. Kansas City won its Super Bowl because Mahomes allowed them to way underspend at the most important position on the field and instead use those dollars to strengthen at more positions.
Take the $5.8M/yr slot for the #3 pick and compare that against the salaries at the various positions. At QB, you're paying the player a backup salary. At DE or WR, you're paying the player a rotational backup salary. At TE, you're paying him a top-15 starter salary. That's terrible value.